Fragmentation inlet for gas chromatography and method of loading a sample thereinto



Oct. 10, 1967 c. STERNBERG 3,346,341

FRAGMENTATION INLE'I FOR GAS CHROMATOGRAPHY AND METHOD OF LOADING A SAMPLE THEREINTO Filed June 28, 1965 FIG. I

{I0 /sa I I FIG. 2

INVENTOR.

JAMES C. STERNBERG ATTO R NEY United States Patent T FRAGMENTATION INLET FOR GAS CHROMA- TOGRAPHY AND METHOD OF LOADING A SAMPLE THEREINTO James C. Sternberg, Fullerton, Calif, assignor to Beckman Instruments, Inc, a corporation of California Filed June 28, 1965, Ser. No. 467,597 12 Claims. (Cl. 23230) The present invention relates to a fragmentation inlet for characterization of a sample composition by fragmentation of the sample into volatile products and subsequent identification of the sample, and more particularly, to both apparatus and a method for placing the sample therein.

A general description of a fragmentation inlet and its use in the field of gas chromatography can be found in copending application Ser. No. 347,744, Sternberg, Fragmentation Apparatus and Method for Characterization of Sample Compositions, filed Feb. 27, 1964, and assigned to the same assignee as the present invention. The prior application deals with the fragmentation of both solid and fluid samples, and with techniques for separating and detecting the products of the fragmentation process. The prior application also deals with the addition of a reactive component gas, such as hydrogen, carbon dioxide, the halogens, hydrogen halide, nitrogen, nitric oxide, or nitrons oxide for stabilization of the discharge potential in a fragmentation device in order to enhance reproducibility.

The device of the present application relates more particularly to a fragmentation inlet designed primarily for the decomposition of solids and high boiling point liquids. Problems with the prior art device have been found in that it has been difficult to precisely locate the sample in the discharge zone, causing reproducibility problems in the fragmentation patterns. Also, large chamber volumes have required excessively high flow rates of gas to sweep out the fragmentated sample molecules and consequent excessive dilution of the sample. Another problem has been the inability to assure that all of the gaseous or vaporized liquid sample would flow through the discharge. Also, the possibility of recombination or secondary fragmentation reactions occurring, due to the fact that the fragmentated molecules were not immediately swept from the discharge zone, presented a problem. Accordingly, it is an object of this invention to provide a fragmentation inlet device for gas chromatography emplOying unique apparatus and methods for sample placement to enhance reproducibility.

Another object of this invention is to provide such an apparatus having a small active volume.

Still another object of the invention is to provide such an apparatus and method wherein the sample containing device is readily detachable for cleaning and mounting in the inlet.

A further object of the invention is to provide such an apparatus and method wherein the sample is placed immediately adjacent an electrode downstream to minimize secondary reactions.

In carrying out the invention, in one form there-of, the sample is placed on a plug of conductive porous material such as carbon felt, contained within a small tube which may be of ceramic, such as alumina. The sample may be held in place by means of a nonconductive plug, such as silica wool; Hollow upstream and downstream discharge electrodes are placed in the ends of the tube, with the downstream electrode contacting the plug. The tube and the electrodes are then mounted in between a nonconductive inlet portion, which may be of ceramic and contains a high voltage contact to the upstream electrode, and an exit portion which may be conductive, grounded, and

3,346,341 Patented Oct. 10, 1967 in electrical contact with the downstream electrode. A pneumatic actuator may be used for readily inserting and removing the sample tube and electrode assembly between the inlet and outlet.

The novel features which are believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof, can best be understood by reference to the following description taken in connection with the accompanying drawing in which:

FIG. 1 is a cross-section diagram of a fragmentation inlet apparatus, in accordance with the present invention, without any sample; and

FIG. 2 is an enlarged view of the sample tube illustrated in FIG. 1, illustrated the placement of the sample in the tube.

Turning now to the drawing, in FIG. 1 a fragmentation inlet is illustrated, including a sample tube 10 which may be of alumina or other nonconducting, temperature resistant material such as silica, and which may be loaded with a sample according to the procedure to be described in connection with FIG. 2. Tube 10 has (inserted in its ends) metal electrodes 12 which may be of platinum, gold, steel or any other good conductive material. Electrodes 12 are held in place by retaining springs 14, located in grooves therein and are hollow, permitting flow of gas through them and through the sample tube 10. This assembly is sealed into an inlet portion 16, which may be of ceramic, and a grounded metal exit portion 18, by means of soft gaskets 20. To provide this seal and yet avoid contamination by organics, gaskets of Grafoil graphite tapes are preferred. This is a flexible graphite material in tape form obtainable from High Temperature Materials, Inc., 31 Antwerp Street, Boston, Massachusetts, and has been found extremely useful in this application. It is available in thicknesses up to 0.010 inches. Other suitable gasket materials are lead and polytetrafiuoroethelyene. Washers of this material give leak-tight seals and no contamination and function properly at making the electrical contacts between the electrode holders and the electrode assemblies. The material is surprisingly inert to oxidation. It is obvious that exit portion 18 could be made nonconductive and other means used to make electrical contact to the associated electrode.

The inlet portion 16 contains a metal contacting pin 22, which serves as a high-voltage contact and makes contact with the electrode assembly through a metallized surface 24 in the inlet 16. This connection may also be made directly to the electrodes by means of a spring contact. The inlet portion 16 also contains a gas inlet tube 26. The gas passes through tube 26, electrodes 12, tube 10, exit portion 18 and exits through an exhaust tube 28. Grounded metal end piece 18 may be moved into or out of scaled contact position by a pneumatic actuator 30. Pressure, introduced at 32, moves end piece 18 through its push rod 34 to seal the assembly, while air pressure introduced at 36 serves to retract grounded end piece 18 and disassemble the apparatus.

The invention includes novel sample handling techniques developed primarily for solid samples and for high boiling point liquids. The dominant variable to be controlled is the location of the sample relative to the electrodes. If the sample is placed adjacent to the downstream electrodes, the electrode 12 in contact with exit portion 18, the volatilized breakdown products are subjected to a minimal amount of discharge and hence, are not further degraded. Larger fragments are thus obtained, and these are essentially those furnished by a thermal pyrolysis. In the case of polyethylene, for example, linear olefins presumably predominate. When the sample tube 10 is ready to be loaded, it is used to cut a disc from a piece of conducting porous material having a rough surface such as graphite or carbon felt, steel wool, fine wire mesh or the like, graphite felt being preferred. Graphite felt is made by heating rayon cloth to a high temperature, for instance 5000 F., and is available from the National Carbon Company, a division of Union Carbide Corporation, 270 Park Ave., New York 17, N.Y. This disc is illustrated at 38 in FIG. 2. The disc 38 is cut With a simple twisting motion of the upstream end of the sample tube 10, or the left-hand end as illustrated in FIG. 1, placed end down on the felt on a firm surface. The felt 38 can then be pushed gently to the desired position within the tube 111. The felt may be laid with its smoother side downwards during cutting so that the smooth side faces up, out of that end of the tube which it occupies immediately after cutting. The felt is pushed in slightly and the sample 40 is placed upon it, approximately centered along the axis of tube 10. The sample 40 can be in the form of a plastic film, a chunk of plastic, powder or granules, for example. A liquid may also be sampled onto an inorganic powder-firebrick, alumina, silica-gel, sand, etc.,and loaded as a solid. A thin layer of nonconductive supporting material 42, such as silica wool or glass wool, may then be placed over the sample 40, most conveniently, by holding the sample tube upright and twisting the top end against the sample of the silica wool, preflamed to remove organics, held with paper or on a finger or thumb. The supporting material may not be necessary. The downstream electrode 12, as illustrated in FIG. 1, is then inserted into the downstream end, or right-hand end in FIG. 1, of the sample tube 10 and the sample sandwich, including graphite felt 38, sample 40 and silica wool 42, is then pushed down into position, pushing the graphite felt 38 gently against the downstream electrode. The upstream electrode, which is the electrode 12 in contact with inlet 16, as illustrated in FIG. 1, is then inserted and the sample is ready for loading into the fragmentation inlet assembly of FIG. 1.

Since it is essential to have the graphite felt end of the sample sandwich downstream, the tube 10 may be marked at one end to be loaded in the downstream direction. It has been found convenient to have a sample tube permanently marked at one end and to start the loading process by introducing the graphite felt 38 into the unmarked end. The felt then properly arrives at the electrode at the marked end when the above sequence of operations is followed.

A desirable variant of the technique is for qualitative identification of efliuents from gas, thin-layer, adsorption or glass-paper chromatography. In the last three techniques, the spot containing the sample is cut, scraped, or otherwise transferred from the chromatogram to the sample tube and analyzed as described for solids. In gas chromatography, the efiluent of the chromatograph is allowed to impinge upon a bed of adsorbent, which may be alumina, silica-gel or other adsorbent, and selected portions of the adsorbent are later transferred to a sample tube for fragmentation as a typical solid sample. In particular, the adsorbent may be moved at known rate under the exhaust vent from the chromatograph, so that peaks on the primary chromatograph can be correlated with the position in the adsorbent bed, and samples may be taken from selected peak locations for qualitative characterization. This technique requires no high temperature valving, yet is simple and versatile.

Advantages of the foregoing techniques include easy sample handling and ready purging of air, as described in the aforementioned copending application, from the sample tube before fragmentation as well as sampling capability in any physical state or state of subdivision. Also, the technique permits a high degree of reproducibility. The sample tubes are readily cleanable, with no cross-contamination, and gas-tight, soft gasket seals are provided with noncontaminating gaskets.

The type of electrical discharge fragmentation employed in the fragmentation inlet described above is an electron bombardment in a range of energies imparting a highly localized high temperature in the sample involved. Although, as stated above, a reactive component, such as hydrogen, nitrogen, etc., may be used as described in the aforementioned copending application to stabilize the discharge potentials, enhancing reproducibility, the technique of sample location described herein minimizes this problem by locating the sample at the downstream electrode. The fact that alumina tubes can be readily flame-cleaned and repeatedly re-used makes them feasible, as far as cost goes, for use in the manner described above.

In one embodiment employing electrode spacing of approximately 030 inch, and a carbon felt and sample thickness of about .06 inch, with an alumina tube having a .19 inch inner diameter, it was found that certain samples run with 100 milliamps RMS, A.C., for 30 seconds give highly reproducible patterns with relative peak heights independent of sample amount and geometry, or form, i.e., powder, film, etc. Using a polyethylene film, obtained in the form of a packaging bag, cut into approximately two millimeter diameter discs and using two-disc samples, which weigh approximately micrograms, a current of 50 milliamps for 15 seconds was employed. Quantitatively, the results were found to be poorly reproducible. A run was then made at milliamps for 15 seconds, with the pattern reproducible on refiring again for 15 seconds at 100 milliamps and yet again, for a third time, but with markedly decreased amplitude, illustrating that even at 100 milliamps, 15 seconds is inadequate. Samples run at 100 milliamps for 30 seconds have all shown less than 1% residual pattern on refiring. Samples of polyethylene and polypropylene, obtained from a plastic bottle and a plastic beaker, show surprisingly pronounced differences and highly reproducible characterizations.

It has also been found feasible to produce a controlled distance of exposure to discharge in the gas phase by insertion of a piece of glass filter paper between the sample 40 and the carbon felt 38. The filter paper disc burns through with the discharge and gives a fixed spacing. Use of such a spacer may be particularly helpful if a controlled extent of hydrogenation is to be carried out by addition of hydrogen to the discharge carrier.

While the principles of the invention have now been made clear, there will be immediately obvious to those skilled in the art, many modifications in structure, arrangement, proportions, the elements and components used in the practice of the invention and otherwise, which are particularly adapted for specific environments and operating requirements without departing from these principles. The appended claims are, therefore, intended to cover and embrace any such modifications within the limits of the true spirit and scope of the invention.

What is claimed to be new and desired to be secured by Letters Patent of the United States is:

1. A fragmentation inlet for gas chromatography comprising:

a sample tube;

upstream and downstream electrodes for insertion in opposite ends of said tube;

a porous conducting material inserted in said tube for placement against said downstream electrode upon which a sample may be positioned;

means for passing carrier gas through said upstream electrode, said tube, said sample, said material and said downstream electrode; and

means for making an electric-a1 connection to each of said electrodes.

2 A fragmentation inlet for gas chromatography comprising:

a sample tube;

upstream and downstream electrodes for insertion in opposite ends of said tube;

a nonconductive inlet portion for connection to said upstream electrode;

an exit portion for connection to said downstream electrode;

an electrical connection to each of said electrodes;

a porous conductive material inserted in said tube for placement against said downstream electrode, upon which a sample may be positioned;

said electrodes having a hollow center and said inlet portion and exit portion each containing a tube such that carrier gas may flow through said inlet portion, said upstream electrode, said tube, said sample, said material, said downstream electrode, and said exit portion.

3. A fragmentation inlet for prising:

a sample tube;

upstream and downstream electrodes provided with gas-tight retaining means for insertion in opposite ends of said tube;

a nonconductive inlet portion for connection to said upstream electrode including an electrical connection to said upstream electrode;

a grounded conductive exit portion for connection to said downstream electrode and electrical contact therewith;

a porous conducting material inserted in said tube for placement against said downstream electrode and upon which a sample may be positioned;

said electrodes having a hollow center and said inlet portion and exit portion each containing a tube such that carrier gas may flow through said inlet portion, said upstream electrode, said tube, said sample, said material, said downstream electrode and said exit portion.

4. The apparatus of claim 3 including pneumatic means for reversibly compressing and releasing said inlet portion, said electrodes, said tube and said exit portion into and out of sealing contact.

5. The apparatus of claim 4 in which graphite washers are inserted between said electrodes and said tube, said inlet portion and said outlet portion in order to provide gas-tight seals.

6. The apparatus of claim 1 in which said porous conducting material is graphite felt and said tube is alumina.

7. The apparatus of claim 1 wherein said sample is a normally volatile material adsorbed on an inorganic solid adsorbent.

8. A fragmentation inlet for prising:

an alumina sample tube;

upstream and downstream electrodes for insertion in opposite ends of said tube;

a graphite felt plug inserted in said tube for placement against said downstream electrodes, upon which a sample may be positioned;

a layer of silica wool placed over said sample;

means for passing carrier gas through said upstream electrode, said tube, said silica wool, said sample, said plug and said downstream electrode; and

means for making an electrical connection to each of said electrodes.

9. A method of loading a sample in a fragmentation inlet sample tube for gas chromatography comprising the steps of:

placing a plug of a conductive porous material in the upstream end of the tube;

placing a sample on the upstream end of the plug;

gas chromatography comgas chromatography cominserting a downstream electrode in the downstream end of the tube;

pushing the plug against the downstream electrode;

and

placing an upstream electrode in the upstream end of the tube.

10. A method of loading a sample in a fragmentation inlet sample tube for gas chromatography comprising the steps of:

rotating the upstream end of a sample tube against a conductive porous material to cut out a plug of the material the size of the tube;

placing a sample on the upstream end of the plug;

placing a layer of nonconducting porous material over the sample;

inserting a downstream electrode in the downstream end of the tube;

pushing the plug against the downstream elecrode;

and

placing an upstream electrode in the upstream end of the tube.

11. A method of loading a sample in a fragmentation inlet sample tube for gas chromatography comprising the steps of:

rotating the upstream end of an alumina sample tube against a sheet of graphite felt to cut out a porous conducting plug the size of the tube;

placing a sample on the upstream end of the plug;

placing a layer of silica wool on top of the sample;

inserting a downstream electrode in the downstream end of the tube;

pushing the plug against the downstream electrode;

and

placing an upstream electrode in the upstream end of the tube.

12. A method of loading a sample in a fragmentation inlet for gas chromatography comprising the steps of:

rotating the upstream end of an alumina tube against a sheet of graphite felt to cut out a porous conducting plug the size of the tube;

placing a sample on the upstream end of the plug;

placing a layer of silica Wool on top of the sample;

inserting a downstream electrode in the downstream end of the tube with a graphite washer therebetween;

pushing the plug against the downstream electrode;

placing an upstream electrode in the upstream end of the tube with a graphite washer therebetween;

placing graphite washers over the exposed ends of the electrodes;

pneumatically compressing the electrodes and the tubes between an inlet portion and an outlet portion in such a manner as to permit flow of a carrier gas through the inlet portion, the upstream electrode, the tube, the silica wool, the sample, the plug, the downstream electrode and the outlet portion; and providing electrical contacts to each of the electrodes.

References Cited UNITED STATES PATENTS 902,607 11/1908 Roberts 204-323 X 1,339,225 5/1920 Rose 204-323 X 1,376,180 4/ 1921 Wickersham 204-323 X 3,167,396 1/ 1965 Staunton et al. 23-253 MORRIS O. WOLK, Primary Examiner.

H. A. BIRENBAUM, R. M. REESE,

Assistant Examiners. 

11. A METHOD OF LOADING A SAMPLE IN A FRAGMENTATION INLET SAMPLE TUBE FOR GAS CHROMATOGRAPHY COMPRISING THE STEPS OF: ROTATING THE UPSTREAM END OF AN ALUMINA SAMPLE TUBE AGAINST A SHEET OF GRAPHITE FELT TO CUT OUT A POROUS CONDUCTING PLUG THE SIZE OF THE TUBE; PLACING A SAMPLE ON THE UPSTREAM END OT THE PLUG; PLACING A LAYER OF SILICA WOOL ON TOP OF THE SAMPLE; INSERTING A DOWNSTREAM ELECTRODE IN THE DOWNSTREAM END OF THE TUBE; PUSHING THE PLUG AGAINST THE DOWNSTREAM ELECTRODE; AND PLACING AN UPSTREAM ELECTRODE IN THE UPSTREAM END OF THE TUBE. 